Solid oxide electrolysis cell with internal heater

ABSTRACT

An individual solid oxide cell (SOC) constructed of a sandwich configuration including in the following order: an in oxygen electrode, a solid oxide electrolyte, a fuel electrode, a fuel manifold, and at least one layer of mesh. In one embodiment, the mesh supports a reforming catalyst resulting in a solid oxide fuel cell (SOFC) having a reformer embedded therein. The reformer-modified SOFC functions internally to steam reform or partially oxidize a gaseous hydrocarbon, e.g. methane, to a gaseous reformate of hydrogen and carbon monoxide, which is converted in the SOC to water, carbon dioxide, or a mixture thereof, and an electrical current. In another embodiment, an electrical insulator is disposed between the fuel manifold and the mesh resulting in a solid oxide electrolysis cell (SOEC), which functions to electrolyze water and/or carbon dioxide.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 371 filing of International Patent ApplicationPCT/US2017/000067, filed Oct. 16, 2017, which claims the benefit of U.S.provisional patent application No. 62/411,792, filed Oct. 24, 2016,which is incorporated in its entirety herein by reference.

GOVERNMENT RIGHTS

This invention was made with U.S. government support under Contract No.NNX15CC43P, awarded by the National Aeronautics and SpaceAdministration. The U.S. Government has certain rights in the invention.

FIELD OF THE INVENTION

In one aspect, this invention pertains to a solid oxide cell (“SOC”),more particularly, to a solid oxide fuel cell (“SOFC”) and to itsreverse embodiment, a solid oxide electrolysis cell (“SOEC”). Even moreparticularly, this invention pertains to a solid oxide fuel cell havingintegrated therein a fuel reformer and to its reverse embodiment, asolid oxide electrolysis cell having integrated therein a heater. Inanother aspect, this invention pertains to a method of generatingelectricity in the solid oxide fuel cell having integrated therein thereformer. In yet another aspect, this invention pertains to a method ofelectrolyzing water, carbon dioxide or a mixture thereof in the solidoxide electrolysis cell having integrated therein the heater.

BACKGROUND OF THE INVENTION

As known in the art, the solid oxide cell (“SOC”) is provided as asandwich assembly having constituent parts in the following order: afuel electrode, a solid oxide electrolyte, and an oxygen electrode, thefuel and oxygen electrodes being connected via an external electricalcircuit. The solid oxide cell is an apparatus that in forward operationprovides for the electrochemical reaction of a fuel, such as hydrogen orcarbon monoxide, with an oxidant, such as oxygen, to produce a DCelectrical current and a chemical product, namely, water or carbondioxide, respectively. The same apparatus in reverse or regenerativeoperation provides for the electrolysis of a fuel, namely water orcarbon dioxide, to produce hydrogen and oxygen in the case of water, oralternatively, carbon monoxide and oxygen in the case of carbon dioxide.

In the SOFC, the fuel is typically provided to the fuel electrode whereit reacts via oxidation with oxide ions to produce the oxidized productand a flow of electrons. The electrons travel via an embedded currentcollector and the external electrical circuit to the oxygen electrodewhere molecular oxygen is reduced to form the oxide ions. During transitthe electrons are available to do useful work. The oxide ions producedat the oxygen electrode diffuse through the solid oxide electrolyte tothe fuel electrode to complete the chemical reaction.

The solid oxide electrolyte typically comprises a ceramic that is a goodconductor of oxide ions but a poor or nonconductor of electrons, whichensures that the electrons pass through the external circuit. As anexample, the solid oxide electrolyte can be constructed of a ceramiccomprising a yttria-stabilized zirconia (YSZ) sandwiched in between afuel electrode comprised of a nickel oxide/YSZ cermet and an oxygenelectrode comprised of a doped lanthanum manganite.

Since each individual SOFC produces only a small, generally low voltage,typically a large number of individual fuel cells are connected inseries to form a stack for the purpose of achieving a higher voltage andcurrent. Each fuel cell stack includes interconnects (or bipolar plates)that separate the individual fuel cells from each other as well as flowmanifolds that deliver and distribute the flows of fuel and oxygen totheir respective electrodes within the stack and remove products fromthe stack. For the purposes of this invention, the term “interconnect”is deemed equivalent to and interchangeable with the term “bipolarplate”. Additionally, as used herein, the term “fuel interconnect” shallrefer to an interconnect disposed on the fuel electrode side of thecell; whereas the term “oxygen interconnect” shall refer to aninterconnect disposed on the oxygen electrode side of the cell. Theinterconnects can be constructed to provide dual functionality as flowmanifolds. Additionally, each fuel cell includes a current collector ateach electrode, either as a separate layer or as integrated into theassociated interconnect. Each individual fuel cell in a stack isfrequently referred to as a “fuel cell repeat unit”.

It should be appreciated that in the aforementioned forward operation,the fuel to the SOFC is provided as gaseous hydrogen or gaseous carbonmonoxide. Since gaseous hydrogen and carbon monoxide requirepressurization and are not readily available as transport fuels, thesegaseous fuels impose limitations on the size and portability of the fuelcell. To solve the problem of gaseous fuel delivery, the prior artdiscloses apparatuses wherein a fuel reformer is integrated with thefuel cell or stack, so as to convert in situ and on demand areadily-available hydrocarbon fuel into a gaseous reformate providingthe hydrogen and carbon monoxide. Certain prior art, for example, U.S.Pat. No. 4,647,516, discloses a reforming catalyst in the form ofpellets or particulates filled into channels or support structures thatare disposed adjacent to the fuel electrode. Particulate catalysts aredisadvantageously cumbersome, weighty and prone to attrition losses.Other prior art, for example, U.S. Pat. No. 6,051,329 and US applicationpublication 2005/0170234, disclose a reforming catalyst that is coatedonto or dispersed into the fuel electrode (referred to as the “anode”)or onto an interconnect adjacent to the fuel electrode. The coated anddispersed designs placed directly on the interconnect and fuel electrodeare difficult to manufacture. Additionally, both prior art designs haveproblems in that reforming capability often interferes with the expectedcapability of the fuel cell part; for example, the oxidation reaction atthe fuel electrode or current collection at the interconnect isdiminished. Moreover, coating the fuel electrode or interconnect with areforming catalyst often diminishes reforming capability, which leads topoisoning of the reforming and fuel cell parts via coking.

It should be further appreciated that start-up of prior art solid oxidefuel cells undesirably involves a significant amount of time. Typically,a supply of preheated oxygen or air is fed to the cell to raise the cellslowly to its operating temperature of between 800° C. and 1,000° C. Aflow of fuel is also started at a designated temperature, and SOFCoperation commences and approaches steady state over time. Once the cellhas reached its steady state operating temperature, withdrawal of heatis required to maintain safe operation and acceptable cell lifetime.Prior art solid oxide fuel cells lack rapid and efficient heat input andheat withdrawal mechanisms.

In regenerative SOEC operation, a fuel, such as water or carbon dioxide,is fed to the fuel electrode where the fuel is reduced with electronsdelivered from an external current source provided to the cell, therebyproducing hydrogen or carbon monoxide, respectively, and oxide ions. Theoxide ions diffuse through the solid oxide electrolyte from the fuelelectrode to the oxygen electrode, where electrons are released toproduce oxygen gas. In this instance the electrons transit through theexternal circuit from the oxygen electrode to the fuel electrode.

Three operating modes are well-known for high temperatureelectrolysis: 1) thermoneutral, 2) endothermal, and 3) exothermal. Hightemperature electrolysis operates at thermal equilibrium when electricalenergy input equals total energy demand, and theoretical electricalconversion efficiency is 100 percent. In the thermoneutral mode, theheat demand (Q) necessary for splitting water or carbon dioxide,calculated as a product of temperature (T) and change in entropy (ΔS),equals heat released by joule heating (ohmic losses) within the cell. Inthe exothermal mode, the electric energy input exceeds the enthalpy ofreaction corresponding to an electrical efficiency below 100 percent. Inthis mode, heat is generated from the cell and can be reused in thesystem to preheat the inlet water and/or carbon dioxide. This mode alsohas the advantage to operate at higher current density resulting inreduced system size; but may, however, lead to premature ageing ofsystem components. Finally, in the endothermal mode the electric energyinput stays below the enthalpy of reaction which means a cell voltagebelow the thermoneutral one. Therefore, heat must be supplied to thesystem to maintain the temperature.

The art discloses heaters disposed adjacent to one or more fuel cellstacks to provide the required heat input for SOEC operation. See, forexample, International Patent Application publication WO 2014/139882.Generally, the disposition of the heaters in prior art apparatuses doesnot provide for uniform heating of each cell repeat unit in the stack.This can result in hot or cold spots in the stack that stress one partof the stack more than another and ultimately either degrade the stackor crack a single or multiple solid oxide cells within the stack.

The art would benefit from design improvements in solid oxide cellrepeat units and stack assemblies having a reformer/heater unitintegrated therewith. Improvements would desirably include a more rapidstart-up of the SOFC/SOEC cell as well as more efficient heat input andheat withdrawal mechanisms, as compared with prior art designs. Otherimprovements would include employment of a more compact, higherefficiency and longer lifetime reformer that minimizes coking at thereformer and the fuel electrode. Yet other improvements would includeoperating at a lower peak fuel cell temperature and providing greateruniformity of temperature within the fuel cell stack, so as to improvethe lifetime of the fuel cell.

It should be appreciated that any SOC system having a reformerintegrated therein should minimize the size of the reformer. Even moreimportantly, the reformer should operate with a conversion efficiencygreater than about 80 percent in a single pass in converting thehydrocarbon fuel to hydrogen and carbon monoxide, else the resultingreformate contains a disadvantageously high concentration of unconvertedhydrocarbon, which at SOFC operating temperatures potentially cokes andcritically damages the fuel electrode.

SUMMARY OF THE INVENTION

In one aspect, this invention provides for a solid oxide cell (SOC)comprising components disposed in a sandwich configuration in thefollowing order:

-   -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold, and    -   (v) at least one layer of mesh disposed adjacent to the fuel        manifold, on a side of the fuel manifold opposite a side facing        the fuel electrode.        In particular exemplary embodiments explained in detail        hereinafter, the solid oxide cell (SOC) of this invention        functions in forward direction as a solid oxide fuel cell        (SOFC), or functions in reverse direction as a solid oxide        electrolysis cell (SOEC), or functions in both forward and        reverse directions dually as a combined SOFC-SOEC.

In one exemplary embodiment, this invention provides for a solid oxidefuel cell (SOFC) having a reformer integrated therein, comprisingcomponents disposed in a sandwich configuration in the following order:

-   -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold, and    -   (v) a reformer comprising at least one layer of mesh having a        reforming catalyst supported thereon, the at least one layer of        mesh disposed in at least one of the following configurations:    -   (1) disposed on at least a portion of the fuel manifold, on a        side of the fuel manifold facing the fuel electrode; and    -   (2) disposed as a fifth aspect of the sandwich configuration        adjacent to the fuel manifold, on a side of the fuel manifold        opposite a side facing the fuel electrode.

In a related aspect, this invention provides for a method of generatingelectricity in the aforementioned solid oxide fuel cell (SOFC) having areformer integrated therein, comprising:

-   -   (a) providing a solid oxide fuel cell comprising components        disposed in a sandwich configuration in the following order:    -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold,    -   (v) a reformer comprising at least one layer of mesh having a        reforming catalyst supported thereon, the at least one layer of        mesh disposed in at least one of the following configurations:    -   (1) disposed on at least a portion of the fuel manifold, on a        side of the fuel manifold facing the fuel electrode; and    -   (2) disposed as a fifth aspect of the sandwich configuration        adjacent the fuel manifold, on a side of the fuel manifold        opposite a side facing the fuel electrode;    -   (b) contacting oxygen with the oxygen electrode under conditions        sufficient to produce oxide ions, the oxide ions diffusing from        the oxygen electrode through the solid oxide electrolyte to the        fuel electrode;    -   (c) at the reformer contacting a gaseous hydrocarbon fuel with        steam, or with an oxidant, or with both steam and an oxidant, in        the presence of the reforming catalyst, the contacting occurring        under reaction conditions sufficient to produce a gaseous        reformate comprising hydrogen and carbon monoxide;    -   (d) distributing the reformate through the fuel manifold; and    -   (e) contacting the reformate with the oxide ions at the fuel        electrode under reaction conditions sufficient to produce water,        carbon dioxide, or a mixture thereof, and an electrical current.

The solid oxide fuel cell of this invention provides a combination ofbenefits not found heretofore in the prior art. First, the fuel cell ofthis invention avoids a need for an external reformer and associatedbalance of plant components including an external heat exchanger;thereby reducing weight, dimensions, and complexity that such externalcomponents add to the fuel cell stack assembly. Second, whereas priorart internal reforming designs dispose the reforming catalyst as aparticulate bed adjacent to the fuel electrode or as a coating bonded toor a solid dispersed within the fuel electrode or fuel interconnect; incontrast, the solid oxide fuel cell of this invention disposes thereformer as a separate catalytic layer of mesh on or adjacent to thefuel manifold. In contrast to prior art designs, the invention isadvantageously tailored to provide for simplified manufacture anduniformity of temperature throughout the cell repeat unit and stackassembly. Moreover, the mesh structure of the invention in a metaland/or otherwise electrically conductive embodiment provides rapid heatinput for start-up of the fuel cell through resistive heating or throughthe exothermic reforming process (CPOX/ATR). Likewise, the mesh providesfor effective heat removal during steady state operation via theendothermic reforming process (SR). Active cooling of the fuel electrodevia the reforming reaction occurring in the mesh adjacent to the fuelelectrode also reduces the required heat removal rate (namely, the rateof oxygen or air flow at the oxygen electrode) resulting in increasedsystem efficiency and reduced parasitic losses. These advantages aid inreducing thermal stress and moderating the temperature of the SOC, whichleads to longer SOC lifetime.

More to the point, the reformer employed in this invention, comprisingthe mesh having supported thereon a reforming catalyst, has demonstratedresistance to carbon formation during steam or partial oxidationreforming of gaseous hydrocarbons. The mesh's low thermal mass providesfor a substantially uniform temperature profile and avoidance ofcarbon-producing cold spots within the reformer. Finally, enhancedgeometric and specific surface areas of the mesh promote improvedconversion of reactants. In comparison to feeding pure hydrogen ormethane directly to the fuel cell, this invention relies on feedinghydrogen and carbon monoxide produced in the embedded reformer,resulting in an increased power density and higher fuel utilization perfuel cell repeat unit. Moreover, the reformer is adaptable to eitherendothermic steam reforming (SR), exothermic catalytic partial oxidation(CPOX), or autothermal reforming (ATR), as desired.

If desired, this invention provides a water neutral apparatus andprocess, in that the water produced during fuel cell operation can becycled to the reformer and utilized in the steam reforming process. Thesubject invention also readily allows for fuel exhaust recycle to thefuel electrode, if desired, while minimizing interference with currentcollection and flow distributors and manifolds. The design is adaptableto solid oxide stacks from various manufacturers.

In another exemplary embodiment, this invention provides for a solidoxide electrolysis cell (SOEC) having a heater integrated therein,comprising components disposed in a sandwich configuration in thefollowing order:

-   -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold,    -   (v) an insulator, and    -   (vi) a heater comprising at least one layer of mesh absent a        catalyst, the heater disposed adjacent to the insulator on a        side of the insulator opposite a side facing the fuel manifold.

In a related aspect, this invention provides for a process ofelectrolyzing a fuel in the aforementioned solid oxide electrolysis cell(SOEC) having a heater integrated therein, comprising:

-   -   (a) providing a solid oxide electrolysis cell comprising a        sandwich configuration in the following order:    -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold,    -   (v) an insulator, and    -   (vi) a heater comprising at least one layer of mesh absent a        catalyst, the heater disposed adjacent to the insulator on a        side of the insulator opposite a side facing the fuel manifold;    -   (b) resistively heating the at least one layer of mesh and        thereby providing heat to the fuel electrode;    -   (c) feeding a fuel through the fuel manifold and contacting the        fuel and a supply of electrons at the fuel electrode under        reaction conditions sufficient to produce a reduced chemical        product and oxide ions, the oxide ions migrating from the fuel        electrode through the solid oxide electrolyte to the oxygen        electrode; and    -   (d) contacting the oxide ions with the oxygen electrode under        conditions sufficient to produce molecular oxygen.

The aforementioned electrolysis cell and process provide for a rapidinput of heat to each individual solid oxide cell with temperatureuniformity, so as to drive the endothermic electrolysis. The cell designminimizes interference with current collection and flow distributors andmanifolds and is readily adaptable to SOC stacks from variousmanufacturers.

DRAWINGS

FIG. 1 depicts an embodiment of an integrated reformer-solid oxide fuelcell of this invention, specifically, of one repeat unit showing a flowpath through the SOFC with an internal reforming section.

FIG. 2 depicts another embodiment of an integrated reformer-solid oxidefuel cell of this invention.

FIG. 3 depicts another embodiment of an integrated reformer-solid oxidefuel cell of this invention.

FIG. 4 depicts another embodiment of an integrated reformer-solid oxidefuel cell of this invention

FIG. 5 depicts a stack assembly comprising a plurality of repeat unitscomprising the integrated reformer-solid oxide fuel cell of theembodiment shown in FIG. 4.

FIG. 6 depicts an embodiment of an integrated heater-solid oxideelectrolysis cell of this invention.

FIG. 7 depicts an embodiment of a solid oxide cell of this invention,particularly of one repeat unit capable of regenerative operation.

DETAILED DESCRIPTION OF THE INVENTION

In basic concept, the solid oxide cell (SOC) described herein is capableof functioning in forward direction as a solid oxide fuel cell (SOFC)and in reverse direction as a solid oxide electrolysis cell (SOEC). Eachsolid oxide cell, which is typically repeated multiple times in eachfuel cell stack, comprises a sandwich configuration in the followingorder:

-   -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold; and    -   (v) at least one layer of mesh disposed adjacent to the fuel        manifold, on a side of the fuel manifold opposite a side facing        the fuel electrode.

In one exemplary embodiment, the at least one layer of mesh supports areforming catalyst capable of either steam reforming (SR), catalyticpartial oxidation (CPOX), or autothermal reforming (ATR). In thisembodiment, the at least one layer of mesh having the reforming catalystsupported thereon provides for a reformer integrated into each SOCrepeat unit in the stack. The resulting repeat unit and fuel cell stackconvert a gaseous hydrocarbon, such as methane, into a gaseous reformatecomprising hydrogen and carbon monoxide, and thereafter convert thereformate and a supply of oxygen into oxidized chemical products,respectively, water and carbon dioxide, and a usable DC electricalcurrent.

In another exemplary embodiment, an electrical insulator configured, forexample, as a gasket or frame is additionally disposed between the fuelmanifold and the at least one layer of mesh. In another exemplaryembodiment, the electrical insulator and the at least one layer of meshare combined into one composite piece by coating the insulator onto theat least one layer of mesh. In these embodiments, the mesh does notsupport a reforming catalyst. The resulting embodiments function as anelectrolysis cell (SOEC), which is capable of electrolyzing water,carbon dioxide or a mixture thereof at the fuel electrode to theirrelated reduced products, respectively, hydrogen, carbon monoxide or amixture thereof. Oxygen is produced as a coproduct at the oxygenelectrode.

In yet another exemplary embodiment, the solid oxide cell comprising theat least one layer of mesh comprises a reforming catalyst supportedthereon and further comprises an electrical insulator configured, forexample, as a gasket or frame disposed between the fuel manifold and theat least one layer of mesh. In this embodiment, the resulting solidoxide cell provides dual or regenerative functionality, in forwarddirection as a solid oxide fuel cell (SOFC) and in reverse direction asa solid oxide electrolysis cell (SOEC). In this dual-functionalembodiment, the solid oxide cell comprises a sandwich configurationhaving components in the following order:

-   -   (i) an oxygen electrode,    -   (ii) a solid oxide electrolyte,    -   (iii) a fuel electrode,    -   (iv) a fuel manifold,    -   (v) an insulator; and    -   (vi) a dual reformer-heater comprising at least one layer of        mesh having a reforming catalyst supported thereon; the at least        one layer of mesh disposed adjacent to the insulator on a side        of the insulator opposite a side facing the fuel manifold.

In yet another embodiment, a plurality of any one of the aforementionedsolid oxide cells of this invention, i.e., individual repeat units, areconnected in series to assemble a solid oxide stack. In anotherembodiment, the solid oxide stack is comprised of at least one of theaforementioned solid oxide cells of this invention and at least one ofany conventional solid oxide cells. In another embodiment, a pluralityof such stacks is assembled into a larger solid oxide cell system.

With reference to FIG. 1, an embodiment of this invention (10) of asingle solid oxide cell (cell repeat unit) (15) having a reformerintegrated therein is depicted, which comprises in sandwichconfiguration the following components: an oxygen interconnect (6), anoxygen electrode (5), a solid oxide electrolyte (4), a fuel electrode(3), a fuel manifold (2), and a reformer comprising at least one layerof mesh (1) having a reforming catalyst (14) supported thereon. Asdepicted in FIG. 1, the fuel manifold (2), also functioning as a fuelinterconnect or fuel bipolar plate, is formed of a solid materialprovided with a flat surface on a side (16) facing the at least onelayer of mesh (1) and further provided with a series of grooves andchannels on an opposite side (18) facing the fuel electrode (3). Thegrooves and channels function to direct and distribute a flow of fuel tocontact the fuel electrode (3). Likewise, the oxygen interconnect (6)also functions as an oxygen manifold by construction as a solid platehaving a series of grooves and channels on a side facing the oxygenelectrode (5), for directing and distributing a flow of oxidant tocontact the oxygen electrode (5) and out of the cell. In the embodimentdepicted in FIG. 1, the grooves and channels of the fuel manifold (2)provide for a reformate flow (8, 9) in transverse or cross-wisedirection with respect to the flow of oxygen (12, 11) as provided by thegrooves and channels in the oxygen interconnect (6). It should beappreciated that the fuel and oxygen manifolds are not limited to flowdesigns consisting of grooves and channels; but may provide a variety ofother operable flow patterns. Alternative flow designs include, forexample, holes, pores, reticulated nets, and any combination thereofincluding with the aforementioned grooves and channels.

In terms of SOFC operation, a flow (7) of steam and a gaseoushydrocarbon fuel, e.g. methane, are fed through the reformer comprisingthe at least one layer of catalytic mesh (1) where the hydrocarbon issteam reformed to produce a gaseous reformate (8) comprising hydrogenand carbon monoxide. The gaseous reformate (8) exiting the mesh reformer(1) is rerouted through the fuel manifold (2), which in in theembodiment of FIG. 1 consists of a plurality of flow channels andgrooves where the reformate contacts the fuel electrode (3), such thathydrogen and carbon monoxide are reacted with oxide ions to form waterand carbon dioxide, which exit with, any unconverted reformate via fuelexhaust flow (9). During the oxidation reaction, electrons are releasedinto an external electrical circuit (not shown) connecting fuelelectrode (3) with oxygen electrode (5). Electrons migrate through theexternal electrical circuit to the oxygen electrode (5) and duringtransit are capable of producing electrical work. At the oxygenelectrode (5), a flow of oxygen or air (12) is fed into the grooves andchannels of the oxygen interconnect (6), where the oxygen is contactedwith and reduced at the oxygen electrode (5) to produce oxide ions. Theoxide ions migrate from the oxygen electrode (5) through the solid oxideelectrolyte (4) to the fuel electrode (3) to complete theelectrochemical reaction. Unconverted oxygen or air exits via flow (11)at the exit side of the channels of the oxygen interconnect (6).

FIG. 2 depicts another embodiment of this invention (20) comprising theintegrated reformer-solid oxide fuel cell of one repeat unit, plus anoxygen interconnect from the next repeat unit. Here, a sandwichconstruction is provided with components in the following order: anoxygen interconnect (26), an oxygen electrode (25), an oxygen-sidegasket (27), a solid oxide electrolyte (24), a fuel electrode (23), afuel-side gasket (28), a fuel manifold (functioning also as fuelinterconnect) (22), a reformer comprising at least one layer of mesh(21) having a reforming catalyst bonded thereon, and the oxygeninterconnect (29) from the adjacent to fuel cell unit. As seen in FIG.2, the mesh reformer (21) is disposed on the side of the fuel manifold(22) opposite the side facing the fuel electrode (23). In FIG. 2, forclarity of illustration, the reformer (21) is depicted as a layerwithout cross-hatching and catalyst; nevertheless, it should beappreciated that the reformer comprises the aforementioned catalyticmesh similar to the embodiment shown in FIG. 1 (1). (The same applies toFIGS. 3-5.) As compared with FIG. 1 where the fuel manifold (2) isconstructed with grooves and channels for directing the flow ofreformate into contact with the fuel electrode (3), in the embodiment ofFIG. 2, the fuel manifold (22) comprises a series of pores and holes fordirecting the flow of reformate into contact with the fuel electrode(23). Gaskets (28, 27) provide seals that ensure that essentially all ofthe appropriate gaseous flows pass into contact with the fuel and oxygenelectrodes (23, 25), respectively.

FIG. 3 depicts another embodiment of this invention (40) comprising anintegrated reformer-solid oxide fuel cell of one repeat unit plus anoxygen interconnect from the next repeat unit. Here again, a sandwichconstruction is provided in the following order: an oxygen interconnect(46), an oxygen electrode (45), an oxygen-side gasket (47), a solidoxide electrolyte (44), a fuel electrode (43), a fuel-side gasket (48),a fuel manifold (also functioning as the fuel interconnect) (42), areformer comprising at least one layer of mesh (41) having a reformingcatalyst supported thereon, plus an oxygen interconnect (49) from theadjacent to fuel cell unit. As seen in FIG. 3, the mesh reformer (41) isdisposed on the side of the fuel manifold (42) opposite the side facingthe fuel electrode (43). In this embodiment, the fuel manifold (42) ismodified such that the reformer inlet and the fuel electrode outlet(anode outlet) are disposed on the same side/plane, which is a variationof the design shown in FIG. 1. The gas distribution is made uniform byaltering the channels design within the fuel manifold (42). Gaskets (48,47) provide seals that ensure that essentially all relevant gaseousflows pass into contact with the fuel and oxygen electrodes (43, 45),respectively.

FIG. 4 illustrates yet another embodiment of the invention (50) whereinthe reformer comprising the at least one layer of mesh (51) having thereforming catalyst supported thereon, is disposed along a leading edgeof the fuel manifold (52) on a side of the fuel manifold (52) facing thefuel electrode (53). The term “leading edge” refers to the edge of thefuel manifold at an inlet to the flow path, as depicted by an arrow inFIG. 4.

FIG. 5 depicts an embodiment of this invention (30) comprising a stack(33) constructed from a plurality of integrated reformer-solid oxidecell units, each unit configured as described hereinabove in FIG. 4.

FIG. 6 depicts an exemplary embodiment (60) of this invention of asingle solid oxide cell integrated with a heater, which functions inSOEC mode. Model (60) comprises in sandwich configuration the followingcomponents: an oxygen interconnect (66), an oxygen electrode (65), asolid oxide electrolyte (64), a fuel electrode (63), a fuel manifold(62), also functioning as the fuel interconnect or fuel bipolar plate, afirst electrical insulator gasket or frame (68), a heater (61)comprising at least one layer of mesh, preferably a metal mesh, and asecond electrical insulator (94) disposed on a side of the mesh (61)opposite a side facing the first electrical insulator (68). In thisembodiment, no catalyst is supported on the mesh. As depicted in FIG. 6,the fuel manifold (62) is formed of a solid material configured with aflat surface on a side facing the first insulator (68) and heater (61),and further configured with a series of grooves and channels on anopposite side facing the fuel electrode (63), the groves and channelsfor directing and distributing a flow (70) of fuel across the fuelelectrode (63) exiting as flow (90). Likewise, the oxygen interconnect(66) is constructed as a solid plate configured with a series of groovesand channels on a side facing the oxygen electrode (65) for directingand distributing a flow (92) of oxygen and optional sweep gas, such asair, through the oxygen interconnect (66) and then exiting the cell asflow (91).

In terms of SOEC operation, the heater (61) comprising the at least onelayer of mesh is heated resistively to provide heat to the cell. Theinsulator gasket (68) provides electrical insulation between the mesh(61) and the electrically conductive fuel manifold (62). A flow of fuel(70), specifically carbon dioxide or water or a mixture thereof, is fedinto the fuel manifold (62), where the fuel contacts the fuel electrode(63) and is electrochemically reduced via input of electrons derivedfrom the electrical circuit to form oxide ions (O²⁻) and a secondchemical product. The second chemical product, which is hydrogen whenthe fuel is water, or carbon monoxide when the fuel is carbon dioxide,exits the channels of the fuel manifold (62) via exit flow path (90).The oxide ions migrate from the fuel electrode (63) through the solidoxide electrolyte (64) to the oxygen electrode (65). At the oxygenelectrode (65), the oxide ions are converted to oxygen which is swept,typically with a flow (92) of a sweep gas, such as air or oxygen orsteam, through the channels of the oxygen interconnect (66), exiting asflow (91). The electrons collected at the oxygen electrode (65) travelvia the external electrical circuit (not shown) to the fuel electrode(63) where they are consumed to complete the electrolysis reaction.

FIG. 7 depicts an embodiment of the SOC of this invention capable ofregenerative operation, wherein solid oxide cell (60) of FIG. 6 havingcomponents described hereinabove further comprises a reforming catalyst(14) supported on the mesh (61), preferably herein a metal mesh, therebyproviding dual-functional heating and reforming. When all or a portionof the at least one layer of mesh (61) supports a reforming catalyst,the cell is capable of operating in forward direction as a SOFC andreverse direction as SOEC. In this embodiment in SOFC operation, thefuel flow (72) is directed towards the reforming catalyst, and thereformate exiting as flow (78) is redirected through the fuel manifold(62), as seen in FIG. 7. This dual functional form of operation is knownas “regenerative” mode.

The aforementioned embodiments of this invention are depicted in theDrawings herein as having a sandwich configuration of planar sheets.Other geometries may be suitable including wherein the planar sheetshave a defined curvature. Generally, it is optimal for each layer in thesandwich configuration to have essentially identical outer dimensionsand surface geometry, so that the layers of the sandwich fit uniformlyagainst each other for thermal and chemical efficiencies.

Regarding materials of construction, the mesh provides a variety ofuseful functions in thin, compact, light-weight sheets. In one aspect,the mesh functions as a catalyst substrate. For this function, a steamreforming (SR) or catalytic partial oxidation (CPOX) or autothermalreforming (ATR) catalyst is supported on the mesh such that theresulting catalytic mesh is capable of converting a gaseous hydrocarbonin the presence of steam and/or an oxidant into a gaseous reformatecomprising hydrogen and carbon monoxide. In another aspect, the mesh asprovided in a metallic or otherwise electrically conductive embodimentfunctions as a resistive heating element that rapidly transmits heatwith substantial uniformity across the mesh to start-up the reformer forSOFC operation as well as to provide heat for operation under stand-byor low load operations. Accordingly, in one embodiment, an externalburner, which is capable of combusting a burner gas, such as hydrogen,carbon monoxide, or methane, to generate heat for start-up of the SOFC,is not necessary and is eliminated. During steady state operation of theSOFC, no further resistive heating is required, and the cell produces anexotherm from the electrochemical reaction. In yet another aspect, whenthe anode/fuel electrode tail gas is recycled to the reformer, the SOFCsystem of this invention further minimizes the duty for an externalburner to provide heat required for the recycling operation. In SOECmode the conductive mesh provides a continuous input of heat viaelectrical resistive heating for endothermic electrolysis reactions.

Each layer of mesh employed in this invention resembles atwo-dimensional reticulated screen or net comprising a plurality of voidspaces (“cells”), with a third dimension comprising anultra-short-channel-length flow path, which in one embodiment is equalto or not much longer than the diameter of the elements from which themesh is made. For the purposes of this invention, the term“ultra-short-channel-length” refers to channel lengths in a range fromabout 25 microns (μm) (0.001 inch) to about 500 μm (0.02 inch). In oneexemplary embodiment, the ultra-short-channel-length ranges from about50 μm (0.002 inch) to about 150 μm (0.006 inch). In contrast, prior artmonoliths represent three-dimensional structures having long flow pathsor channels running there through, such long channels referring to achannel length greater than about 1 mm (0.039 inch), and often greaterthan about 5 mm (0.20 inch).

More specifically, each layer of mesh in this invention typically isconfigured with a plurality of channels or pores having a diameterranging from about 0.25 millimeters (mm) to about 1.0 mm, with a voidspace greater than about 60 percent, preferably up to about 80 percentor more. A ratio of channel length to diameter is generally less thanabout 2:1, preferably less than about 1:1, and more preferably, lessthan about 0.5:1. Preferably, the ultra-short-channel-length mesh has acell density ranging from about 100 to about 1,000 cells or flow pathsper square centimeter.

In terms of materials of construction, the layers of mesh can beselected each individually from metals, non-metals, such as ceramics,and mixtures of ceramics and metals including cermets. The choice ofmesh is tailored to the application. For SOFC operation solely, thelayers of mesh are not-restricted, and any of metals, ceramics, andmixtures thereof are suitable. For SOEC operation solely, the layers ofmesh are each individually constructed from metals or analogouselectrically-conductive materials capable of providing for resistiveheating. For regenerative operation in both SOFC and SOEC modes, thelayers of mesh are each individually constructed from metals oranalogous electrically-conductive materials capable of providingresistive heating. The mesh is not limited by any method of manufacture;for example, meshes can be constructed via weaving or welding fibers, orby an expanded metal technique as disclosed in U.S. Pat. No. 6,156,444,incorporated herein by reference, or by 3-D printing, or by a lostpolymer skeleton method.

In more specific exemplary embodiments, the metal mesh is constructedfrom any conductive metal or combination of metals provided that theresulting structure is capable of withstanding the temperatures andchemical environment to which it is exposed. Suitable non-limitingmaterials of construction for the metal mesh include iron-chromiumalloys, iron-chromium-aluminum alloys, and iron-chromium-nickel alloys.

Such metal meshes are available commercially, for example, from AlphaAesar and Petro Wire & Steel. In one embodiment, the metal meshcomprises a Microlith® brand metal mesh obtainable from PrecisionCombustion, Inc., of North Haven, Conn., USA. As described in U.S. Pat.Nos. 5,051,241 and 6,156,444, incorporated herein by reference,Microlith® brand mesh technology offers a unique design combining anultra-short-channel-length with low thermal mass in one monolith, whichcontrasts with prior art monoliths having substantially longer channellengths as noted hereinabove.

The term “ceramic” refers to inorganic non-metallic solid materials witha prevalent covalent bond, including but not limited to metallic oxides,such as oxides of aluminum, silicon, magnesium, zirconium, titanium,niobium, and chromium, as well as zeolites and titanates. Reference ismade to U.S. Pat. Nos. 6,328,936 and 7,141,092, detailing insulatinglayers of ultra-short-channel-length ceramic mesh comprising wovensilica, both patents incorporated herein by reference. The term “cermet”refers to a composite material comprising a ceramic in combination witha metal, the composite being typically conductive while also exhibitinga high resistance to temperature, corrosion, and abrasion in a mannersimilar to ceramic materials.

As compared with prior art monoliths, the mesh having theultra-short-channel-length facilitates packing more active surface areainto a smaller volume and provides increased reactive area for a givenpressure drop. Whereas in prior art honeycomb monoliths havingconventional long channels, a fully developed boundary layer is presentover a considerable length of the channels; in contrast, theultra-short-channel-length characteristic of the mesh useful for thisinvention avoids boundary layer buildup. Since heat and mass transfercoefficients depend on boundary layer thickness, avoiding boundary layerbuildup enhances transport properties. The advantages of employing themesh having the ultra-short-channel-length, and preferably, theMicrolith® brand thereof, to control and limit the development of aboundary layer of a fluid passing there through is described in U.S.Pat. No. 7,504,047, which is a Continuation-In-Part of U.S. Pat. No.6,746,657, both patents incorporated herein by reference.

In another exemplary embodiment, the mesh is constructed of an analogousstructure of metal, ceramic, or other manufactured or structuredultra-short-channel-length substrate material comprising aninterconnected network of solid struts defining a plurality of pores ofan open-cell configuration. The pores can have any shape or diameter;but typically, a number of pores that subtend one inch designates a“pore size,” which for most purposes ranges from about 5 to about 80pores per inch. The relative density of such structures, taken as thedensity of the structure divided by the density of solid parent materialof the struts, typically ranges from about 2 to about 15 percent.Manufactured or structured ultra-short-channel-length substrates arecommercially available in a variety of materials capable of withstandingthe operating temperatures of the SOFC and SOEC of this invention.

In the solid oxide cell of this invention, it is desirable to employfrom 1 to about 10 layers of mesh per SOC repeat unit. In anotherembodiment, from 1 to about 4 layers of mesh are employed per SOC repeatunit. It should be appreciated that when present, the reforming catalystin one embodiment is applied to each layer of mesh. Alternatively, inanother embodiment the reforming catalyst is applied to at least one butnot all of the mesh layers present. As an example, it is possible to use3 layers of mesh, wherein the middle layer is coated with a reformingcatalyst, while the top and bottom layers are not.

In another exemplary embodiment, the loading of the reforming catalyston the mesh is varied along the length of the mesh layer in thedirection of fuel flow, thereby providing a catalyst concentrationgradient along the direction of fuel flow. In yet another embodiment,the catalyst is loaded onto the mesh in a predetermined patternsufficient to provide a predetermined thermal gradient across the meshunder reforming conditions. Both of these embodiments provide a methodof controlling temperature during the reforming process while minimizingthermal stresses on the solid oxide cell. More specifically, in oneembodiment, the loading of the reforming catalyst increases along thelength of the mesh in the direction of fuel flow. In another embodiment,the loading of the reforming catalyst increases from an inlet of thefuel flow to a maximum at about a mid-point of the length of the mesh inthe direction of fuel flow, and then decreases from the mid-point to theend of the mesh at the outlet of the fuel flow.

The disposition of the mesh in each fuel cell repeat unit is envisionedin several different embodiments. In one embodiment, the mesh isprovided on at least a portion of the fuel manifold on a side of thefuel manifold facing the fuel electrode. One way to implement thisembodiment involves positioning the mesh in at least one layer at theleading edge of the fuel manifold. The term “leading edge” refers to aninlet edge of the flow manifold where fuel is fed into the manifold. Incontrast, the term “trailing edge” refers to an exit edge of the fuelmanifold where product gases exit the SOC. Another embodiment involvespositioning the mesh in and along channels or grooves of the fuelmanifold. As an example, strips of mesh can be disposed in at least aportion of the channels and grooves of the fuel manifold, preferablyalong the length of the channels and grooves from the leading edge tothe trailing edge. There is no limitation on the manner in which thelayer(s) of mesh are disposed on the fuel manifold. Many other operableembodiments can be envisioned besides those mentioned hereinabove.

In another embodiment, at least one layer of mesh is positioned adjacentto the fuel manifold, on a side of the fuel manifold opposite a sidefacing the fuel electrode. In another embodiment, at least one layer ofmesh is positioned adjacent to an electrical insulator, which itself ispositioned adjacent to the fuel manifold. Both the electrical insulatorand the mesh are disposed on a side of the fuel manifold opposite a sideof the fuel manifold facing the fuel electrode.

Any catalyst capable of converting a hydrocarbon fuel, either by steamreforming (SR), or catalytic partial oxidation (CPOX), or autothermalreforming (ATR) into a gaseous mixture comprising hydrogen and carbonmonoxide (synthesis gas) is suitably supported for catalytic purposes onthe mesh, particularly, by coating the catalyst onto the mesh. Suchcatalysts include at least one metal selected from Group VIII metals ofthe Periodic Table, including iron, cobalt, nickel, ruthenium, rhodium,palladium, osmium, iridium, platinum, and combinations thereof.Preferably, the catalyst is selected from the platinum group metals(PGM) including ruthenium, rhodium, palladium, osmium, iridium,platinum, and combinations thereof. In one embodiment, the catalyst issupported on an oxide washcoat, suitable non-limiting species of whichinclude titania (TiO₂, e.g., anatase and rutile phases), silica (SiO₂),magnesia (MgO), alumina (Al₂O₃), zirconia (ZrO₂), and mixtures thereof.The catalyst, with or without the oxide washcoat, is bound to the meshby any conventional coating preparation method known in the art.

Materials useful for the fuel and oxygen electrodes should be stable atoperating temperatures; should have a coefficient of thermal expansioncompatible with that of the solid oxide electrolyte; and should bechemically compatible with the solid oxide electrolyte and othermaterials during fabrication and operation of the solid oxide cell.Functionally, in forward operation, the job of the fuel electrode is tocombine the oxide ions that diffuse through the electrolyte with thegaseous reformate fuel supplied to the fuel electrode to produce waterand carbon dioxide as well as a flow of electrons. Typically, the fuelelectrode is constructed of a porous ceramic layer that allows thegaseous reformate to flow uniformly throughout from inlet to outlet.Since the fuel electrode must be electrically and ionically conductive,the fuel electrode typically comprises a combination of ceramic andmetal (cermet) prepared by standard ceramic processing techniques.Non-limiting examples of cermets useful as the fuel electrode includenickel-yttria stabilized zirconia, i.e., Ni—Y₂O₃ stabilized ZrO₂(Ni—YSZ), nickel mixed with gadolina doped ceria,Ni—[(CeO₂)_(0.8)(GdO₂)_(0.202)] also written as Ni—(Ce,Gd)O₂ orNi-(GDC), nickel mixed with yttria doped ceria zirconiaNi—[Y₂O₃—(CeO₂)_(0.7)(ZrO₂)_(0.3)] also written as Ni-YDCZ, and nickelmixed with yttria doped zirconia (Ni—Y-stabilized ZrO₂) also written asNi—YSZ. Other suitable fuel electrode materials include strontiumvanadium molybdenum oxide (Sr₂VMoO₆₋₈) and lanthanum strontium manganesechromium oxide (LSCM) [(La_(0.75)Sr_(0.25))Mn_(0.5)Cr_(0.5)O₃).

The solid oxide electrolyte comprises a dense layer of ceramic thatconducts oxide ions (O²⁻). As an example of a material from which thesolid oxide electrolyte layer can be made, we include yttria-stabilizedzirconia (YSZ), scandia-stabilized zirconia (ScSZ), andgadolinium-stabilized ceria (GDC), as well as ceria-based electrolytesof the florite structure and lanthanum gallate (LSGM) of a perovskitecrystalline structure. As newer electrolytes are developed, these maylead to less resistivity problems and improved conductivity of oxideions, which in turn may lead to more robust and better performingelectrolyte layers, any of which may be employed in this invention.

The oxygen electrode should also be porous so as to provide for auniform flow of oxygen throughout the electrode and should be capable ofconducting oxide ions (O²⁻) to the solid oxide electrolyte. Asnon-limiting examples of a material from which the oxygen electrode canbe formed, we include manganese-modified-yttria-stabilized zirconia(Mn—YSZ), lanthanum strontium manganite (LSM), lanthanum strontiumferrite (LSF), (La,Sr)(Co,Fe)O₃ and any of the cobalites.

It should be appreciated that this invention is in no way limited by thethickness of any of the layers of the fuel electrode, the solid oxideelectrolyte, or the oxygen electrode. The thickness of any layer dependsin part on whether the solid oxide cell is “electrode supported” or“electrolyte supported”. The term “supported” refers to the layers thatprovide structural strength to the cell. Other suitable supports include“metal supported” cells. Typically, the greater the reliance onstructural strength, the thicker is the layer. Thus, a solid oxide cellmay be constructed wherein the fuel or oxygen electrode is thickest andthe electrolyte layer is thinnest. Alternatively, a solid oxide cell maybe constructed wherein the electrolyte layer is thickest and the fueland oxygen electrodes are thinner.

Each individual solid oxide cell of this invention produces less thanabout 1 V under typical operating conditions in SOFC mode, but most SOFCapplications require higher voltages. Accordingly, for most practicalapplications a plurality of individual SOC repeat units of thisinvention is connected electrically in series to form a stack, so as toobtain a higher voltage required for the application. The stack isconstructed by securing each SOC repeat unit between two interconnectsthat provide strength to the stack and separate the repeat units fromeach other.

Since the interconnects are exposed at high temperatures to bothoxidizing and reducing sides of the fuel cell, the interconnects shouldbe highly stable. Accordingly, the interconnects are comprised of anyelectrically conductive material that can withstand the thermal andchemical environment to which they are exposed. In one embodiment, theinterconnects are constructed of metallic plate or foil, for example,high temperature stainless steels, such as SS446, SS430, AL454, E-Brite,Crofer 22, or iron chromium (FeCr) alloys or nickel chromium (NiCr)alloys. In another embodiment, the interconnects are constructed fromcermets (metal doped ceramics) which provide for acceptable thermalstability and electrical conductivity. This invention is not limited toany particular interconnect thickness and materials.

It should be appreciated that the fuel-side interconnect forms anadditional layer distinctly different from the mesh layer(s) of thisinvention supporting the reforming catalyst and functioning as reformerand heater. Accordingly, in any solid oxide stack, there is typicallydisposed in each SOC at least one layer of mesh in accordance with thisinvention and at least one layer or constructs of conventionalinterconnect(s), which based on design may function additionally as afuel manifold and/or current collector. The current collector may be anyelectrically conductive material, typically metallic, and preferably, asilver or copper screen.

Since each SOC repeat unit in the stack is sandwiched between twointerconnects, gaskets are provided around the edges of each repeat unitto provide for a gas-tight seal. The gaskets are typically made of aceramic (not doped with metal), or glass, or a rubbery seal.

Other parts, such as separators and insulators, can be formed from anysuitable material that can withstand the temperature and chemicals towhich the parts are exposed. The electrical insulator, required incertain embodiments of this invention, is formed from any electricallynon-conductive material including heat resistant ceramics that are notdoped with metals.

In forward SOFC operation, the hydrocarbon fuel fed to the reformercomprises any hydrocarbon that exists in a gaseous state at about 22° C.and about 1 atm (101 kPa) pressure or any liquid hydrocarbon that isreadily vaporized and fed as a vapor to the reformer. Non-limitingexamples of such gaseous hydrocarbons include methane, natural gas,ethane, propane, butane, biogas, and mixtures thereof. Non-limitingexamples of liquid hydrocarbons that are readily vaporized includehexane, octane, gasoline, kerosene, and diesel. If steam reforming (SR)is desired, then a flow of liquid water is disposed in thermal contactwith the stack so as to utilize the heat of the stack to produce therequired steam, which is then fed with the hydrocarbon gas to thereformer. A molar ratio of steam to carbon in the hydrocarbon fuel (S/Cratio) typically ranges from about 1.5:1 to about 4.0:1 during steadystate operation. If the reformer operates as an exothermic process, thena flow of oxidant comprising air or oxygen is supplied with the gaseoushydrocarbon to the reformer, with steam (ATR) or without steam (CPOX).The oxidant additionally may comprise other oxygen-bearing components,such as, carbon dioxide. The relative amount of oxygen atoms in theoxidant to carbon atoms in the gaseous hydrocarbon fuel (O/C ratio), asfed to the reformer, typically ranges from about 0.1:1 to about 1.3:1,but should preferably be “fuel-rich” or higher in atomic carbon contentthan atomic oxygen content so that little, if any, of the hydrocarbonfuel is converted to carbon dioxide and water. It should be appreciatedthat when an oxidant is employed, then the apparatus is designed, viaO/C ratio or other means, to minimize contact of the oxidant with thefuel electrode, so as to avoid damaging the electrode. In one embodimentthe SOFC is started up on a mixture of hydrocarbon fuel, such asmethane, and oxygen until a steady state operating temperature isreached, at which time the SOFC is transitioned to steam reforming on amixture of hydrocarbon fuel and steam. If desired, recycle of the fuelelectrode exhaust gas (anode tail gas), optionally, with a smallquantity of oxygen can be implemented.

Generally, the SR reformer operates at a temperature close to thetemperature of the fuel electrode, that is, typically between about 500°C. and about 1,000° C. CPOX reformers operate at a somewhat highertemperature between about 700° C. and about 1,100° C. The overallpressure of the solid oxide fuel cell ranges typically from about 1 bar(100 kPa) to about 5 bars (500 kPa). In SOFC operation, the weighthourly space velocity of the total gaseous flow to the reformertypically ranges from about 250 liters per hour per gram catalyst(L/h/g-cat) to about 6,000 L/h/g-cat.

In either SR, CPOX or ATR operation, the reformer output to the fuelelectrode is a gaseous reformate comprising hydrogen and carbon monoxide(synthesis gas), although a large quantity of nitrogen may be present ifair is used as the oxidant. Other byproducts in acceptably smallquantities include one or more of carbon dioxide, water, and methane.The mesh reformer employed in this invention produces minimal quantitiesof unconverted hydrocarbons thereby resulting in minimal coke formation,a longer catalyst lifetime, and less degradation of the reformer andSOC. It should be appreciated that the conversion of the hydrocarbonfuel in the reforming stage is governed by equilibrium concentrations atthe operating temperature. Nevertheless, the mesh reformer of thisinvention is capable of achieving a hydrocarbon conversion efficiency ofgreater than about 80 percent, and even greater than about 90 percent,relative to an equilibrium efficiency of 100 percent, in one passthrough the reformer at operating temperatures of 650° C. or higher.Moreover, the mesh reformer employed in this invention is capable ofoperating for up to 1,000 hours without any observable degradation inperformance of the reforming catalyst. Additionally, the reformer ofthis invention can be cycled through multiple start-ups and shut-downswithout degrading performance.

In SOEC operation, the fuel provided to the fuel electrode compriseswater, carbon dioxide, or a mixture thereof. The fuel may containunreactive components, such as hydrogen. Electrons are provided via anexternal DC circuit. A sweep gas, such as air or an inert gas including,for example, nitrogen or helium, is typically employed to remove theoxygen produced from the cell. Operating temperatures, pressures, andspace velocities are similar to those specified hereinabove for SOFCoperation.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions, or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

The invention claimed is:
 1. A solid oxide electrolysis cell having aheater integrated therein, comprising components disposed in a sandwichconfiguration in the following order: (i) an oxygen electrode, (ii) asolid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel manifold,(v) an insulator, and (vi) a heater comprising at least one layer ofmesh absent a reforming catalyst, the at least one layer of meshdisposed adjacent the insulator, on a side of the insulator opposite aside facing the fuel manifold.
 2. The solid oxide electrolysis cell ofclaim 1 wherein the at least one layer of mesh each individually has anultra-short-channel-length ranging from greater than 25 microns to lessthan 500 microns and a cell density ranging from 100 to 1,000 cells persquare centimeter.
 3. The solid oxide electrolysis cell of claim 1wherein from 1 to 10 layers of mesh are employed, optionally, providedin a planar configuration.
 4. The solid oxide electrolysis cell of claim1 wherein the mesh is constructed from a metal mesh.
 5. The solid oxideelectrolysis cell of claim 1 wherein the insulator is configured in theshape of a frame or gasket.
 6. The solid oxide electrolysis cell ofclaim 1 wherein the insulator is selected from non-conductive ceramics.7. The solid oxide electrolysis cell of claim 1 further comprising asecond insulator adjacent the at least one layer of mesh, on a side ofthe mesh opposite a side facing the insulator referenced in claim 1(v).8. The solid oxide electrolysis cell of claim 1 wherein the insulatorreferenced in claim 1(v) and the heater (vi) are combined into acomposite such that the insulator (v) is provided as a coating on the atleast one layer of mesh.
 9. The solid oxide electrolysis cell of claim 1wherein the fuel manifold is constructed with a plurality of grooves andchannels, or with a plurality of holes and pores, or a combinationthereof.
 10. The solid oxide electrolysis cell of claim 1 wherein the atleast one layer of mesh comprises a structured material having from 2 to80 pores per inch and a density ranging from 2 to 15 percent, relativeto density of a parent material from which the structured material isconstructed.
 11. The solid oxide electrolysis cell of claim 1 whereinthe fuel electrode is selected from nickel-yttria stabilized zirconia,nickel mixed with gadolina doped ceria; nickel mixed with yttria dopedceria zirconia, strontium vanadium molybdenum oxide, and lanthanumstrontium manganese chromium oxide, and mixtures thereof.
 12. The solidoxide electrolysis cell of claim 1 wherein the solid oxide electrolyteis selected from yttria-stabilized zirconia, scandia-stabilizedzirconia, gadolinium-stabilized ceria, ceria-based electrolytes of theflorite structure, and lanthanum gallate of a perovskite crystallinestructure, and mixtures thereof.
 13. The solid oxide electrolysis cellof claim 1 wherein the oxygen electrode is selected frommanganese-modified-yttria-stabilized zirconia, lanthanum strontiummanganite, lanthanum strontium ferrite, cobalites, and mixtures thereof.14. A solid oxide stack comprising at least one solid oxide electrolysiscell as defined in claim
 1. 15. A process of electrolyzing a fuel in asolid oxide electrolysis cell having a heater integrated therein,comprising: (a) providing a solid oxide electrolysis cell comprisingcomponents disposed in a sandwich configuration in the following order:(i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuelelectrode, (iv) a fuel manifold, (v) an insulator, and (vi) a heatercomprising at least one layer of mesh absent a reforming catalyst, theheater disposed adjacent the insulator, on a side of the insulatoropposite a side facing the fuel manifold; (b) resistively heating the atleast one layer of mesh and thereby providing heat to the fuelelectrode; (c) feeding a fuel through the fuel manifold and contactingthe fuel and electrons at the fuel electrode under reaction conditionssufficient to produce a reduced chemical product and a coproduct ofoxide ions, the oxide ions migrating from the fuel electrode through theelectrolyte to the oxygen electrode; and (d) contacting the oxide ionswith the oxygen electrode under conditions sufficient to producemolecular oxygen.
 16. The process of claim 15 wherein the fuel compriseswater and hydrogen is produced at the fuel electrode.
 17. The process ofclaim 15 wherein the fuel comprises carbon dioxide and carbon monoxideis produced at the fuel electrode.
 18. The process of claim 15 whereinthe at least one layer of mesh each individually has anultra-short-channel-length ranging from greater than 25 microns to lessthan 500 microns and a cell density ranging from 100 to 1,000 cells persquare centimeter.
 19. The process of claim 15 wherein under operatingconditions overall pressure ranges from 100 kPa to 500 kPa; and weighthourly space velocity of the total gaseous flow to the reformer rangesfrom 250 liters per hour-gram catalyst (L/h-g-cat) to about 6,000L/h-g-cat.
 20. The process of claim 15 wherein under operatingconditions temperature ranges from 500° C. and 1,000° C.
 21. The processof claim 15 wherein a sweep gas comprising air or an inert gas isemployed to remove the molecular oxygen from the cell.
 22. The processof claim 15 wherein the mesh is constructed from a metal mesh,optionally, provided in a planar configuration.